1. Technical Field
The present disclosure relates to an electronic device capable of charging an internal battery and having power supplied from an external source, and more particularly to an electronic device that can be connected to an external device.
2. Related Art
Electronic devices that can operate using power supplied from an internal battery typically turn the power off when the battery becomes discharged and the output voltage drops in order to prevent faulty operation. In such electronic devices, a rush current is produced when the power turns on. A problem that can occur when this happens is that the rush current causes a temporary drop in the supply voltage, and this drop in the supply voltage causes the power to turn off. To prevent the power from turning off due to the rush current produced when the power turns on, JP-A-H01-047231 discloses technology that ignores this drop in the supply voltage when the power turns on.
In electronic devices that can receive power from an external source and can recharge an internal battery, power supply capacity of the connected external source may be unknown. If a current supply exceeding the power supply capacity of the external power source is received from such an external power source, the output voltage of the external power supply drops. A method for preventing faulty operation or failure of the electronic device when this happens is to monitor the output voltage of the external power supply and control the upper limit of the current supplied from the external power supply to prevent a drop in the output voltage of the external power supply. For example, when the electronic device detects a drop in the output voltage of the external power supply, the electronic device lowers the upper current limit from the present level, thereby preventing the output voltage from dropping and protecting the electronic device.
However, the conventional electronic device described above has a problem that if the rush current is high while an external device is connected, the capacity of the external power supply cannot be used effectively.
For example, when a specific memory card is inserted into the electronic device and the rush current to the memory card is high, current exceeding the normal current consumption of the electronic device flows for a certain time even if the memory card is normal. When this happens, the conventional electronic device detects a drop in the output voltage of the external power supply and lowers the maximum current limit. Depending on the actual external power supply capacity and the threshold level of the input current limit, unnecessary protection may thus be applied. As a result, only current up to the reduced limit is supplied, and it takes more time to charge the battery, so that effectively using the capacity of the external power supply may not be possible.